Todas as informações são descritas na página do manual :
De man youtube-dl
--audio-quality QUALITY
ffmpeg/avconv audio quality specification, insert a value between 0
(better) and 9 (worse) for VBR or a specific bitrate like 128K (default 5)
-f, --format FORMAT
video format code, specify the order of preference using slashes, as in -f
22/17/18 . Instead of format codes, you can select by extension for the
extensions aac, m4a, mp3, mp4, ogg, wav, webm. You can also use the special
names "best", "bestvideo", "bestaudio", "worst".